This invention relates to tone generators and more particularly to tone generators for providing single or multiple tones.
Telephone signaling requirements often include the use of a number of tone frequencies used singly or in combination over transmission links such as in a Touch Tone telephone system. Thus, both telephone and telegraph carrier systems require multiple tone sources.
Presently telephone and telegraph signaling systems employ both RC (resistor capacitor) and LC (inductor capacitor) type oscillators of a variety of configurations to produce the desired tones. RC type tone generators are often not stable enough for some applications, although they do have the advantage that integrated circuit techniques can be employed with this type of circuit for miniaturization. In contrast, the LC type circuits can be designed to be stable enough, however, the coils are often bulky, and do not lend themselves to miniaturization by integrated circuit techniques. Both types of generators suffer in that in production, there is required the individual tuning of each tone frequency and that they require alignment or retuning as part of the maintenance procedure.